Oracle SQL Developer Data Modeler Version 18.104.22.1683
Anyone tell me where to find the templates for defining patterns for Keys, Indexes and Constraints?
In version 3 it used to be in Tools > General Options > Naming Standards > Templates
In version 22.214.171.1243 you should open the Properties Dialog for the Design (by right-clicking over the entry for the relevant Design in the Browser tree and selecting Properties).
Then in the Design Properties dialog select Settings > Naming Standard > Templates